This invention relates to internal combustion engines, and more particularly, the invention relates to an idle control for an internal combustion engine.
Internal combustion engines have a torque for a particular RPM that varies based upon several parameters. For spark ignition internal combustion engines, the torque varies based upon ignition of the air/fuel mixture relative to crankshaft rotation or piston position within the combustion chamber. An engine produces a maximum amount of torque at approximately 35xc2x0 before the piston reaches top dead center of the combustion chamber for a particular RPM. Operating an engine at maximum torque for a particular RPM is desirable so that the most amount of torque is available at any given moment.
It is desirable to idle an engine at the lowest RPM at which the engine is able to ran stable for increased fuel efficiency. However, at lower RPMs the speed of the engine may fluctuate causing the engine to run xe2x80x9croughxe2x80x9d due to load fluctuations. For example, as an air conditioning compressor cycles on and off while the engine is idling the speed may fluctuate causing the engine to idle rough due to the load fluctuations from the compressor. As a result, the spark is typically retarded to approximately 10xc2x0-15xc2x0 before top dead center so that torque is available to overcome these load fluctuations. The engine controller varies the spark to vary the engine torque and overcome the load fluctuations. Overcoming load fluctuations by increasing or decreasing the air flow through the throttle above is not practical since there is an undesirable amount of time between the throttle actuation and the response of the engine. Spark control of the engine provides a response time that is approximately ten times greater than that of throttle control.
Unfortunately, the maximum torque for that particular RPM is no longer available since the spark is retarded. As the load on the engine increases at idle, such as when the compressor turns on, the spark is advanced so that the engine torque increases thereby overcoming the increased load caused by the compressor. In this manner, engine idling stability is increased so that engine smoothness is improved. Therefore, what is needed is an engine idle control that enables the engine to be run at the maximum torque for the particular engine RPM so that the greatest amount of torque is available at any given moment.
The present invention provides an internal combustion engine having a crankshaft which rotates at an actual crankshaft speed. An accessory drive is driven by the crankshaft and includes an accessory drive component, such as an alternator, which produces a load on the crankshaft. A speed sensor senses an engine speed associated with the actual crankshaft speed and produces a speed signal. A controller sends a control signal to the accessory drive component in response to the speed signal to change the load of the accessory drive component and maintain the actual crankshaft speed at a target crankshaft speed. If the actual speed is greater than the target speed, the duty cycle of the accessory drive component may be increased to put a greater load on the engine and lower the actual speed toward the target speed. Conversely, if the actual speed is lower than the target speed, the duty cycle of the accessory drive component may be decreased to decrease the load on the engine and increase the actual speed toward the target speed. As a result, spark control of the engine is not required to overcome load fluctuations so that the engine may be run at the maximum torque for the particular engine speed. If sufficient control of the engine speed is not possible by changing the load of the accessory drive component alone, the throttle may also be changed to overcome the load fluctuations of the engine and assist the control provided by the accessory drive component.
Accordingly, the present invention provides an engine idle control that enables the engine to be run at the maximum torque for the particular engine RPM so that the greatest amount of torque is available at any given moment.